By micro-dissection of embryonic brain, norepinephrine-producing cells of the nucleus locus coeruleus and substantia nigra dopamine producing cells can be explanted and maintaned in culture for several weeks. The growth of these brain stem explants are monitored by assaying for catecholamines (CA) with the sensitive radio-enzyme assay. More than half of the locus coeruleus cultures contain measureable (greater than 10 pg) quantitites of norepinephrine and dopamine; reserpine added to the media 10 to the minus 5th power M) depleted both amines. Both brain stem cultures released large amounts of CA into the media. It was concluded that brain stem cultures synthesize CA at a very high rate. The cultured neurons develops normally by growing axons and dendrites, and by making synaptic contacts with each other, although the CA-containing neurons may have a deficit in storage capacity or regulation of CA synthesis. Nevertheless, locus coeruleus explant cultures are a suitable preparation for studies of the development and characterization of norepinephrine-mediate synaptic events.